Sunday
Jul292012

Improving RTLSDR reception

Yes, a better antenna would help...

Serveral years ago, I bought a Motorola broadband signal booster (part #484095-001-00) to solve a weak signal problem with my cable TV reception. The problem subsequently having been resolved, the signal booster sat in a closet. Today I decided to try it between the rabbit ear antenna I am using  and the RTLSDR dongle. The results were quite dramatic. The manufacturer claims a 15 db gain between 52 and 1001 Mhz, and I can concur that I am seeing every bit of those results. Weak stations are coming in much stronger, and I am discovering new stations that were non existent before. Strong stations are now all at -10 db. Definetely worth the price ($35 at Best Buy), as this is a rugged device meant for outdoor installation. A cheaper alternative might be an indoor model, such this RCA 10 db amplifier ($15). And I am quite keen to try this Winegard HDA-200, which claims a 24 db gain.

For the uninitiated, a 15 db gain is a 32 fold increase in signal strength (10 raised to the power of 15/10), while a 24 db gain is a 251 fold increase in signal strength (10 raised to the power of 24/10).  I will advise how it goes, and yes, I have another dongle still in the package if I blow this one out with too much signal!

By the way, with all this weight hanging off the RTLSDR dongle, it would be wise to get a USB hub with a fairly long cable, so that the dongle can lay flat on a surface rather than struggle to stay attached to a PC or laptop USB port. If you have ever opened one up, you have seen it would not take much for the USB connector to break off the circuit board.

Saturday
Jul282012

Release of K5DEV SDRSharp Fork

For the impatient

Download  (Version 1.1.1 Jul 28 2012, 706 KB)
Source code (Version 1.1.1 Jul 28 2012, 267KB)
Provides a frequency manager, scanner, and autosave of some settings at program exit.
At  Youssef' Touil's request, and in order to comply with the MSIL license of SDRSharp that essentially restricts its redistribution, I have removed the files behind the links. The frequency manager is now part of the latest builds of SDRSharp, and saving of settings has been added. I will be developing scanner functionality for my own use and may release it here in a couple weeks.

Details

This release adds two new collapsible panels, "Frequency Manager" and "Scanner", as well as a few internal changes.

The Frequency Manager allows you to store frequencies, as well the associated offset, mode, center frequency, bandwidth and a user provided name and groups. Groups, such as "Police", "Fire & EMS" and "2m Ham",  allow you to display related entries together. Entries are stored in "%LOCALAPPDATA%/SDRSharp/frequencies.xml" in XML format. %LOCALAPPDATA% is a Windows enviroment variable that defines the location for local application data, and its location varies depending on the version of Windows used. For example, on Windows 7, it is typically found in "c:\users\username\AppData\Local".

The Scanner allows you to scan the selected spectrum for activity on any of the stored frequencies found within the selected spectrum. Its operation is controlled by two variables, the linger delay and signal level. The signal level defines the minimum signal level needed to trigger a channel change. The linger delay, which can be set to a value between 0 and 5000 milliseconds, defines how long a channel can be inactive before it is considered to be no longer transmitting. A higher value will prevent a scanner channel switch in mid sentence or mid conversation.

The program was also modified to remember a few settings, so that the next time it is started, it can resume where it last left off. The currently remembered settings are the current front end device, frequency, mode, center frequency, filter bandwidth, audio gain, FFT resolution, contrast of the waterfall display, zoom of the spectrum display,the window size and position, the position of the spectrum/waterfall splitter, the currently selected frequency manager group, the afore mentioed scanner settings and the collapsed/expanded state of each collapsible panel. Settings are stored in XML format in "%LOCALAPPDATA%\SDRSharp\SDRSharp.xml". Finally, the behavior of the collapsible panels was changed so that clicking any part of the title bar (rather than just the label text) toggles the panel.

 

 

Monday
Jul162012

Hacking SDR#: preview of frequency manager and scanning

One of the most requested features in SDR# is the ability to save settings, manage frequencies and scanning functionality. I have taken a few steps towards these wishes, see the video below for a preview.

The Frequency Manager functionality is essentially done. The scanning functionality still needs more work, as you can see from the video, it is too quick to switch off a transmitting frequency (after no activity for 100ms). It also needs some settings, such as the db threshold, rather than the hard coded settings in use now.

The scanning functionality works by monitoring a 2Mhz segment of spectrum for activity on the known frequencies, as defined in the frequency manager. This allows it to be very fast and responsive, since the FFT buckets in which to look for data, given that the center frequency does not change, can be predetermined when scanning starts. In the example in the video, the program only monitors 13 of the 4096 bytes it receives 480000 times a second.

I expect to polish this up this week and release a version with source code next week.

Sunday
Jul152012

Software Defined Radio on the Cheap

Introduction

Software Defined Radio experimentation has been getting cheaper with the advent of front ends such as the FunCube dongle ($175) or the Softrock SDR ($70, kit). An even more compelling solution are SDRs using Realtek RTL2832U/Elonics E4000 based USB DVB-T tuners. USB DVB-T tuners are used to receive digital TV broacasts in Europe, but with the right drivers and software, can be repurposed to receive radio signals in the 64Mhz to 1.7 Ghz range. With an appropriate downconverter, DC to 50Mhz is also possible. Best of all, DVB-T dongles are cheap (less than $30), widely available (the SDRs mentioned above are frequently out of stock) and ready to use out of the box (no soldering required, unlike the Softrock).

Harware

I use the Ezcap 666 USB 2.0 DVB-T/DAB/FM dongle, procured from Ebay, specifically from seller 'noelec' who has sold more than 250 of them for $27.75 including shipping.

Although the unit comes with a small antenna, you may prefer something more robust, as even a "rabbit ears" TV antenna will result in better reception. To do this, you will need a "European TV adapter", Radio shack part number 278-261 (shown on the right attached to the dongle), as well as a TV antenna. If you would rather connect your Jpole of VHF/UHF beam, look for a MCX DVB to SMA adapter. In my experience, with the stock antenna, you will hear a lot of strong public service stations and some strong repeaters. A cheap rabbit ears antenna is enough to pick up most local repeaters.

Finally, you will need a sufficiently powerful PC to connect the dongle to. I use an Intel i7 based laptop, and the software described below uses less than 10% of CPU. I have heard of some people having success with netbooks, I guess it just depends on whether you want to use your PC for anything else while listening.

Software

Software is available for Windows, Mac and Linux. In this post, I concentrate on Windows, although I may cover Mac installation in a future post.

You will not need the drivers (if any) that ship with the dongle. Instead you will need a program called Zadig, a Windows installer for USB device drivers. You will also need an SDR program, such as WinSDR, HDSDR or SDR#. I highly recommend SDR#, for its ease of installation and the availability of source code in C#, something I have already put to good use by adding a frequency manager and scanning functionality. Detailed installation instructions are available here, and will result in a working system, ready for hours of fun.